In a silicon carbide (SiC) semiconductor device, the area of a region around the periphery of a cell (i.e., active) region can be made small, because silicon carbide has high electric field strength. Therefore, as disclosed in JP-A-2001-291860, a silicon carbide semiconductor device can have a large cell region compared to a silicon (Si) semiconductor device, when the semiconductor devices have the same chip size. This is one advantage of using silicon carbide.
However, in a silicon carbide semiconductor device in chip form, a distance from a surface electrode formed in the cell region to a chip edge is short. Therefore, when a vertical power semiconductor element such as a Schottky barrier diode is formed in the cell region, a surface discharge may occur between the surface electrode and the chip edge at the time a negative voltage such as a surge voltage is applied to the surface electrode. As a result, the power semiconductor element may be broken.
The surface discharge is described below with reference to FIG. 7. FIG. 7 is a diagram illustrating a cross-sectional view of a silicon carbide semiconductor device having a Schottky barrier diode (SBD) 100 formed in a cell region. As shown in FIG. 7, the semiconductor device includes a n+-type substrate 101, a n−-type drift layer 102 formed on a front surface of the substrate 101, an oxide film 103 formed on the drift layer 102, a Schottky electrode 104 that is in contact with the drift layer 102 through an opening 103a of the oxide film 103, and a wiring electrode 105 formed on the Schottky electrode 104. The Schottky electrode 104 and the wiring electrode 105 form an anode of the SBD 100. A p-type reduced surface field (RESURF) layer 108 is formed in a surface portion of the drift layer 102 to surround a Schottky contact region where the Schottky electrode 104 is in Schottky-contact with the drift layer 102. A back electrode 107 as a cathode of the SBD 100 is formed on a back surface of the substrate 101. A passivation film 106 is formed to cover the periphery of the Schottky electrode 104 and the wiring electrode 105. In a structure shown in FIG. 7, a surface discharge is likely to occur between the anode and a chip edge, because a distance X from an inner edge of an opening 106a of the passivation film 106 to the chip edge is short.